Geochemistry of Hydrocarbons in Cambrian- and Ordovician-Age Reservoirs, Homer Field, Rome Trough, Eastern Kentucky

Harris, David C.¹, Robert C. Burruss², Robert T. Ryder², D. Jarvie³, and Cortland F. Eble^4
1 Kentucky Geological Survey, University of Kentucky, Lexington, KY
² U.S. Geological Survey, Reston, VA
³ Humble Geochemical Services, Houston, TX
⁴ Kentucky Geological Survey, University of Kentucky, Lexington, KY

Hydrocarbons are produced from three zones in the Homer field, located in the Rome Trough, Elliott County, Kentucky. The Cambrian Rome Formation/Conasauga Group, the Middle Ordovician St. Peter Sandstone, and the Middle Ordovician Trenton Limestone produce natural gas and condensate from 20 wells. Gas samples from 8 wells have BTU contents ranging from 1037 to 1150 (average=1098). The Cambrian and Ordovician reservoirs have very similar gas compositions, averaging 86.9% methane, 3.54% nitrogen, and 0.09% CO².

Condensates from all zones in the Homer field have similar as chromatographic characteristics. These include odd-carbon predominance in the n-alkane C₁₅ to C₁₉ range, and minor amounts of pristane and phytane, similar to hydrocarbons sourced from the Ordovician alga Gloecapsomorpha prisca. Rocks with total organic carbon values up to 4.4% occur in the Rogersville Shale (Conasauga Group), Wayne County, West Virginia, and in the Rome Formation in Garrard County, Kentucky. Bitumen extracts from these shales are similar to Homer field condensates. G. prisca has not been identified in the Cambrian Rogersville Shale, but it contains vitrinite-like macerals very similar to organic matter in the Cambrian Alum Shale of Scandinavia. Reflectance of macerals in the Rogersville Shale is 1.42 Ro%, indicating thermal maturity in the lower wet gas window.

Geochemical similarity of Homer field hydrocarbons to extracts from organic shales within the Conasauga suggests that the Homer field was sourced from Cambrian shales within the Rome Trough. These hydrocarbons also migrated along faults into shallower Ordovician reservoirs, including the St. Peter Sandstone and fractured Trenton Limestone.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004